A voltage regulator circuit is used to convert one supply voltage into another supply voltage. For instance, an integrated circuit may have an internal power supply voltage of 3.3 volts but may have an external power supply voltage of 5.0 volts. As a result, this integrated circuit needs a circuit that converts the external power supply voltage of 5.0 volts to an internal power supply voltage of 3.3 volts. One solution has been to use a pair of closed loop amplifiers. One low current amplifier works in standby mode and a high current amplifier in active mode. They control an output transistor in series with a voltage divider circuit. The feedback loop compares a node of the voltage divider circuit with a reference voltage. One problem with this solution is that it does not respond quickly to load current transients. These load current transients can occur when suddenly large amount of activity starts for example during an address switching or when chip goes from standby to active mode.
Another solution that has been used is a closed loop amplifier system in standby mode and non-linear amplifier system in active mode for fast response. This solution increases the response time of the voltage regulator but introduces switching noise and jitter.
Thus there exists a need for voltage regulator that has a fast response time and has improved stability.